FIG. 11 illustrates the configuration of a conventional signal transmission system based on the DVI standard. In FIG. 11, reference numerals 2601, 2602, and 2603 denote transition minimized differential signaling (hereinafter abbreviated as “TMDS”) encoders/serializers provided at a transmitting side. Also, reference numerals 2604, 2605, and 2606 denote TMDS decoders/recovery units provided at a receiving side.
As illustrated in FIG. 11, in a conventional signal transmission system STSc, red, green, and blue component signals SR, SG, and SB are supplied to the TMDS encoders/serializers 2601, 2602, and 2603, respectively. The TMDS encoders/serializers 2601, 2602, and 2603 respectively TMDS-encode and then serialize the supplied component signals SR, SG, and SB, and send the resultant serial signals to a transmission path TP. Then, at the receiving side, the received serialized signals are TMDS-decoded by the TMDS decoders/recovery units 2604, 2605, and 2606 for recovering the component signals SR, SG, and SB.
A data enable signal DE is a signal that is indicative of a period during which any of the component signals SR, SG, and SB exists and becomes HIGH when active. For example, the period during which the data enable signal DE is LOW coincides with a horizontal synchronizing signal period or a vertical synchronizing signal period. Also, four types of control signals CTL0, CTL1, CTL2, and CTL3 are reserved, but are not used in the present DVI standard. Specifically, the levels of the control signals CTL0, CTL1, CTL2, and CTL3 are always 0.
At the transmitting side, the TMDS encoders/serializers 2601, 2602, and 2603 each convert the video signal (SR, SG, and SB) supplied by 8 bits into a signal of 10 bits, and then serialize the resultant signal for output to the transmission path TP. An object of 8-bit/10-bit conversion is to make data in an appropriate form that is suitable for high-speed transmission by reducing the number of changing points in the data. Also, the TMDS encoders/serializers 2601, 2602, and 2603 respectively convert the 2-bit control signals CTL0, CTL1, CTL2, and CTL3 into a 10-bit signal for output to the transmission path TP.
The TMDS encoders/serializers 2601, 2602, and 2603 each encode and serialize the data enable signal DE for output as serial data to the transmission path TP.
The TMDS decoders/recovery units 2604, 2605 and 2606 at the receiving side decode the 10-bit serial data received from the transmission path TP into the 8-bit red, green, and blue component signals SR, SG, and SB, the data enable signal DE, and the 2-bit control signals CTL0, CTL1, CTL2, and CTL3 for expansion.
However, the DVI standard is directed only to video signal transmission. Therefore, the conventional signal transmission system is not intended to provide a comfortable user interface that enables transmission of information, such as closed-captions or teletext, caption broadcasting, host control information and connection information, etc.
Therefore, an object of the present invention is to provide a signal transmission system that complies with the DVI standard and enables the transmission of closed-captions or teletext together with a video signal, and also transmits a control signal for controlling a host.